The present invention relates to under voltage lockout (UVLO) circuits and specifically to current-mode UVLO circuits.
Under voltage lockout circuits are commonly employed to monitor a power supply and to provide a signal representing the quality of the power supply. Initial application of power to an integrated circuit therefore begins with the UVLO circuit generating an output signal that initially indicates that the power supply is insufficient, such that power is prevented from being supplied to the remainder of the integrated circuit. The UVLO circuit monitors the power supply voltage and in response to the power supply voltage reaching a threshold value switches the signal representation from a ‘supply bad’ state to a ‘supply good’ state that indicates to the remainder of the integrated circuit that initialization processes may begin. The UVLO circuit continues to monitor the power supply and in response to the power supply falling below a threshold value provides an output signal that represents that the power supply is too low and thereby prevents power from being provided to a connected device or circuit. In this way, the anomalous behavior and current consumption of connected circuits caused by low-voltage conditions is prevented.
Typical UVLO circuits rely on comparisons of the power supply voltage to a threshold voltage to determine whether the signal is good or bad (i.e., of sufficient magnitude). However, the power supply may include a large range of voltages (e.g., 0-30 Volts) that requires the UVLO circuit to be capable of handling large voltages. Similarly, the UVLO circuit must be capable of generating a threshold voltage that is supply, temperature, and process independent and that can be used as a reference value to which the supply voltage is compared. In particular, band-gap voltage sources are often constructed to supply the stable and temperature independent voltage source used as a reference voltage. However, UVLO circuits capable of handling large voltage ranges increase the cost and space requirements for UVLO circuits.